The present invention relates generally to ground proximity warning systems and methods and, more particularly, to ground proximity warning systems and methods having a reduced set of input parameters in order, for example, to enhance the situational awareness of the pilots of general aviation aircraft in a cost effective manner.
An important advancement in aircraft flight safety has been the development of ground proximity warning systems, also known as terrain awareness systems. These warning systems analyze the flight parameters of the aircraft and the terrain surrounding the aircraft. Based on this analysis, these warning systems provide alerts to the flight crew concerning possible inadvertent collisions of the aircraft with surrounding terrain or other obstacles, including instances in which the flight path of the aircraft would appear to bring the aircraft in short of the runway.
Ground proximity warning systems often have several modes in order to provide various types of alerts depending upon the flight conditions. For example, the enhanced ground proximity warning system provided by AlliedSignal Inc. has six primary modes of operation. Mode 1 is designed to provide alerts for an aircraft having an excessive descent rate that is relatively close to the underlying terrain. Mode 2 provides an alert in instances in which an aircraft is closing with the terrain at an excessive rate, even in instances in which the aircraft is not descending. Mode 3 provides alerts in instances in which an aircraft loses significant altitude immediately after take off or during a missed approach. Mode 4 provides alerts for insufficient terrain clearance based upon the phase of flight and the speed of the aircraft. In this regard, Mode 4 provides alerts based upon different criteria depending upon whether the aircraft is in the take off phase of flight or in the cruise or approach phases of flight and further depending upon whether the gear is in a landing configuration. Mode 5 also provides two levels of alerts when the aircraft flight path descends below the glideslope beam on front course instrument landing system (ILS) approaches. Finally, Mode 6 provides alerts or call-outs for descent below predefined altitudes or the like during an approach, as well as alerts for excessive roll or bank angles.
In addition to the various modes of operation, the enhanced ground proximity warning system provided by AlliedSignal Inc. defines an alert envelope and, more particularly, both a caution envelope and a warning envelope. The imaginary alert envelopes move with the aircraft and are constructed to extend forwardly of the aircraft and to define a region in which alerts will be generated if terrain or other obstacles enter by penetrating one of the alert envelopes. In this regard, U.S. Pat. No. 5,839,080 to Hans R. Muller et al. and assigned to AlliedSignal Inc. describes an advantageous ground proximity warning system that generates an alert envelope. The contents of U.S. Pat. No. 5,839,080 are hereby incorporated by reference in their entirety.
As described by U.S. Pat. No. 5,839,080, an alert envelope is defined by a number of parameters, including a look ahead distance (LAD), a base width (DOFF) and a terrain floor (xcex94H). In general terms, the look ahead distance defines the distance in advance to the aircraft that the alert envelope extends. Similarly, the terrain floor typically defines a vertical distance below the aircraft which is utilized during the construction of the floor of the alert envelope. Further, the base width is the lateral width of the alert envelope at a location proximate the aircraft.
As described by U.S. Pat. No. 5,839,080, the ground proximity warning system can construct a pair of alert envelopes, namely, a caution envelope and a warning envelope. While each envelope has a similar shape as described above, the caution envelope typically extends further ahead of the aircraft than the warning envelope and is therefore generally larger than the warning envelope. Accordingly, the ground proximity warning system will generate cautionary alerts in instances in which the upcoming terrain or other obstacles penetrate the caution envelope, but not the warning envelope. Once the upcoming terrain or other obstacles penetrate the warning envelope, however, the ground proximity warning system will generate a more severe warning alert. As such, a pilot can discern the severity of the alert and the speed with which evasive maneuvers must be taken in order to avoid the upcoming terrain or other obstacles based upon the type of alert that is provided, i.e., a less severe cautionary alert or a more severe warning alert.
In addition to the various modes of operation and the alert envelopes described above, ground proximity warning systems can also provide other types of alerts. For example, the enhanced ground proximity warning system provided by AlliedSignal Inc. also provides a terrain clearance floor (TCF) alert. In particular, the enhanced ground proximity warning system creates an increasing terrain clearance envelope around an intended runway and alerts are provided if the flight path of the aircraft penetrates the terrain clearance floor, thereby providing alerts if the flight path of the aircraft indicates that the aircraft may land short of the runway. See, for example, U.S. patent application Ser. No. 09/496,296, entitled xe2x80x9cApparatus, Method, and Computer Program Product for Generating Terrain Clearance Floor Envelopes about a Selected Runwayxe2x80x9d filed Feb. 1, 2000 and U.S. patent application Ser. No. 09/454,924, entitled xe2x80x9cMethods, Apparatus and Computer Program Products for Automated Runway Selectionxe2x80x9d filed Dec. 3, 1999 (hereinafter the ""924 application) which describe the generation of a terrain clearance floor and the selection of the runway about which the terrain clearance floor is constructed, respectively. The contents of both of these applications are herein incorporated by reference in their entirety.
While ground proximity warning systems have substantially improved the situational awareness of flight crews of commercial aircraft by providing a variety of alerts of upcoming situations that merit the attention of the flight crews and by providing graphical displays of the upcoming terrain, obstacles and other notable features, ground proximity warning systems generally require a relatively robust set of input parameters. For example, conventional ground proximity warning systems require a signal indicative of the radio altitude from a radio altimeter, signals indicative of the altitude, the computed airspeed, the corrected altitude, the altitude rate, the true airspeed and the static air temperature from an Air Data Computer (ADC), signals indicative of the position, the magnetic track and the corrected altitude from a Flight Management System (FMS), signals indicative of the acceleration, attitude, altitude, vertical speed, position, magnetic heading/track, true heading/track and ground speed from an inertial reference system (IRS) and/or an attitude heading reference system (AHRS), signals indicative of the position, position quality, altitude, ground speed, ground track, date, time and status from a global navigation positioning system (GNSS) or a global positioning system (GPS) (hereinafter collectively referenced as a GPS), signals indicative of the glideslope deviation, a localizer deviation and the selected runway coordinates from an instrument landing system (ILS) and/or a microwave landing system (MLS) as well as other signals from other avionic subsystems. Therefore, for a conventional ground proximity warning system to be fully functional, the aircraft must not only carry the ground proximity warning system, but must also have a number of other subsystems, such as a radio altimeter, an ADC, an FMS, an IRS or an AHRS, a GPS and an ILS or a MLS. As will be apparent, each of these subsystems is quite expensive. However, most large commercial aircraft are mandated to have most, if not all, of these subsystems, such that the input parameters required by a conventional ground proximity warning system are readily available.
In contrast to commercial aircraft, general aviation aircraft, such as light turbine and piston aircraft, are not required to have many of the foregoing subsystems and, as a result, do not carry most of the foregoing subsystems since each subsystem is quite expensive. For example, most general aviation aircraft do not include a radio altimeter or an ADC. In addition, most general aviation aircraft do not include a glideslope receiver and do not provide any signals indicative of the configuration of the landing gear or flaps, as many aircraft have a fixed down landing gear. Even though GPS is becoming increasingly more affordable and many general aviation aircraft therefore carry GPS equipment, conventional ground proximity warning systems cannot function properly based upon the parameters provided solely by the GPS, such as the position, position quality, altitude, ground speed, ground track, date, time and status, without input from a variety of other subsystems that are not generally carried by general aviation aircraft.
General aviation aircraft typically fly at much lower altitudes and in much closer proximity to the underlying terrain and other obstacles than commercial aircraft and would therefore appear to have at least as great, if not greater, of a need for a ground proximity warning system and the various alerts provided by ground proximity warning systems. However, general aviation aircraft cannot generally support a ground proximity warning system since the general aviation aircraft does not carry the other subsystems that would be required in order to provide the ground proximity warning system with the necessary input parameters.
The ground proximity warning system and method of the present invention are designed to provide a number of alerts based upon a substantially reduced set of input parameters. Thus, the ground proximity warning system and method of the present invention can greatly improve the situational awareness of a flight crew without requiring that the aircraft carry a number of other subsystems for providing the robust set of input parameters demanded by conventional ground proximity warning systems. The ground proximity warning system and method of the present invention is therefore particularly well suited for general aviation aircraft that have a GPS receiver, but that do not include a radio altimeter, an ADC or the like.
The ground proximity warning system and method of the present invention include a processor, responsive to a GPS receiver, for determining a positional relationship between an aircraft and upcoming terrain. According to the present invention, the processor is capable of determining the positional relationship between the aircraft and the upcoming terrain based only upon a pressure altitude, signals provided by the GPS and elevational data associated with the upcoming terrain. For example, the GPS signals may include at least one and, more typically, each of the following signals: latitude, longitude, ground speed, ground track, GPS altitude and a quality parameter. In addition, the processor can be responsive to a temperature probe and runway data. In this embodiment, the processor is therefore capable of determining the positional relationship between the aircraft and the upcoming terrain based upon the external air temperature in addition to the pressure altitude, the GPS signals and the elevational data associated with the upcoming terrain.
The ground proximity warning system and method of one embodiment also determines the positional relationship between the aircraft and a runway, typically the runway upon which the aircraft intends to land. According to this embodiment, the processor is capable of determining the positional relationship between the aircraft and the runway based only upon the pressure altitude, the GPS signals and data associated with the runway. Thus, the ground proximity warning system and method of this embodiment can detect instances in which the aircraft may land short of the runway based upon the positional relationship between the aircraft and the runway.
Accordingly, the ground proximity warning system and method of the present invention is capable of functioning with a dramatically reduced set of input parameters relative to conventional ground proximity warning systems and methods. In this regard, the ground proximity warning system and method of the present invention can determine the positional relationship between the aircraft and the upcoming terrain and, in some instances, between the aircraft and an intended runway in a manner independent of at least one and, more typically, each of the following signals: radio altitude, indicated air speed, roll angle, the respective positions of the landing gear and flaps and the glideslope. As such, the ground proximity warning system and method of the present invention do not require an aircraft to also include a number of other relatively expensive subsystems in order to provide the robust set of input parameters demanded by conventional ground proximity warning systems and methods. Thus, the ground proximity warning system and method is well suited for general aviation aircraft which are not required to have radio altimeters, ADCs or the like.
A ground proximity warning system and method of the present invention also include a warning mechanism for providing an alert, if the processor determines that the positional relationship between the aircraft and the upcoming terrain and/or the intended runway fails to meet an alert criteria. In this regard, the ground proximity warning system can also include a memory device for storing a terrain database defining the elevational data for the upcoming terrain and, in some instances, a runway database providing data associated with the intended runway. As such, the processor can construct a warning envelope extending in advance of the aircraft which can then be compared to the elevational data associated with the upcoming terrain such that a warning alert is provided if the upcoming terrain pierces the warning envelope. Likewise, the processor can construct a caution envelope extending further in advance of the aircraft than the warning envelope and can compare the caution envelope to the elevational data associated with the upcoming terrain such that a cautionary alert can also be provided if the upcoming terrain pierces the caution envelope. Further, the processor can determine the geometric altitude of the aircraft as well as the difference between the geometric altitude and the elevation of the local terrain such that an alert can be provided if the difference between the geometric altitude and the elevation of the local terrain is less than a predetermined altitude. Thus, the ground proximity warning system and method of this embodiment can provide callouts at different altitudes above the underlying terrain, such as during an approach.
The ground proximity warning system and method of the present invention can also provide alerts analogous to the alerts provided in several of the modes of a conventional ground proximity warning system and method. For example, a ground proximity warning system and method of one embodiment can provide an alert if the aircraft is determined to have an excessive descent rate at a relatively low altitude in a similar fashion to a Mode 1 alert provided by a conventional ground proximity warning system and method. In this embodiment, the ground proximity warning system determines a pseudo radio altitude and a vertical velocity and thereafter determines if the vertical velocity of the aircraft at the particular pseudo radio altitude exceeds a predetermined sink rate and, if so, preferably activates a warning mechanism for providing an alert. More particularly, the ground proximity warning system and method of this embodiment determine the pseudo radio altitude based upon a geometric altitude and the elevation of local terrain. Since the geometric altitude is typically associated with a figure of merit, the alerts provided by the ground proximity warning system and method of this embodiment are preferably disabled if the pseudo radio altitude is less than the figure of merit, thereby preventing potentially erroneous alerts from being generated. The ground proximity warning system and method of this embodiment also preferably determine the vertical velocity based upon a combination of a first vertical velocity derived from a signal indicative of pressure altitude and a second vertical velocity derived from GPS signals. Thus, the ground proximity warning system of this embodiment can determine a reliable vertical velocity even though the ground proximity warning system and method are typically independent of an IRS or an AHRS that otherwise would provide the vertical speed of the aircraft.
A ground proximity warning system and method according to another embodiment of the present invention detects a descent following takeoff from a runway in order to provide an alert in much the same fashion as alerts provided by a conventional ground proximity warning system and method operating in Mode 3. In this regard, the ground proximity warning system and method of this embodiment include a processor, responsive to a signal indicative of the pressure altitude and to GPS signals, but independent of a radio altitude, for determining height above field, typically based upon geometric altitude values. In addition, the processor determines if an altitude loss of the aircraft at the height above field on takeoff exceeds a predetermined altitude loss and, if so, actuates a warning mechanism for providing an alert. In order to avoid nuisance alerts, the warning mechanism is preferably disabled if the height above field is less than a figure of merit associated with the geometric altitude. Likewise, the warning mechanism is preferably disabled once the height above field is at least as great as a predetermined threshold.
According to the present invention, the embodiments of the ground proximity warning system and method that provide alerts for an excessive sink rate and for excessive descent after takeoff are capable of providing the alerts based solely upon pressure altitude, GPS signals and elevational data association with the respective runways and the local terrain. In addition, the ground proximity warning system and method of these embodiments can also be responsive to a temperature probe such that the pseudo radio altitude and the height above field and also based upon the external air temperature.
While the ground proximity warning system and method of these embodiments are capable of providing the desired alerts in response to only a limited set of input signals, the ground proximity warning system and method of these embodiments are also capable of processing the available signals and providing the desired alerts in the manner independent of many of the signals required by conventional ground proximity warning systems, such as signals indicative of the radio altitude, the indicated airspeed, the roll angle, the respective positions of the landing gear and flaps and the glideslope. Thus, the ground proximity warning systems and methods of these embodiments of the present invention provide alerts that are analogous to the alerts provided by the various modes of conventional ground proximity warning systems and methods without requiring that the ground proximity warning system and method of the present invention interface with as many other subsystems in order to supply the requisite input parameters.
Therefore, the ground proximity warning system and method of the present invention provide alerts in various predefined situations in order to substantially increase the situational awareness of a flight crew without requiring the robust set of input parameters demanded by conventional ground proximity warning systems and methods. Instead, the ground proximity warning system and method of the present invention are capable of providing various alerts based only upon signals representative of the pressure altitude and the GPS signals without reference to a radio altimeter, an ADC, a glideslope receiver or signals indicative of the configuration of the landing gear or flaps. Thus, aircraft, such as general aviation aircraft, can install the ground proximity warning system and method of the present invention in order to provide increased situational awareness and alerting to a possible controlled flight into terrain (CFIT) situation without having to buy and install a number of other subsystems, such as a radio altimeter, an ADC and a glideslope receiver, that are not generally required for general aviation aircraft and that are prohibitively expensive.